Otolith shape analysis has been often widely used for stock discrimination. Controversial results are concluded on geographical stocks between the Crozet Islands and the Kerguelen Islands, East Antarctic. In this study, six otolith shape indices (form factor, roundness, circularity, rectangularity, ellipticity, and aspect ratio) and elliptical Fourier coefficients were used to analyze the otoliths shape of Patagonian toothfish Dissostichus eleginoides (TOP) from those two regions to try to supplement the information about the stocks. Prior to analysis, the allometric effect of fish growth on the otolith morphology was examined. The principal component analysis (PCA) was used for analyzing the shape indices (SIs), the Ellipse Fourier coefficients (EFCs), and the combination of SIs and EFCs, and the success rate of classification is 51.00 %, 74.00 %, and 80.00 % for those three treatments, respectively. The overall otolith shapes of D. eleginoides from the Kerguelen Islands and the Crozet Islands are similar, although fine differences occur in the outer contours of otolith. Combined with the tagging and genetic data, the present study concluded that stock connectivity occurs for TOP between the Crozet Islands and the Kerguelen Islands. Multiple approaches, including otolith chemistry, may help elucidate the proportion and mechanism of exchange between two regions.

The otolith morphology of fish species varies ontogenetically. In this study, 120 otoliths collected from the Ross Sea, the Amundsen Sea, the Weddell Sea, and the Lazarev Sea were used to analyze the morphological differences in otolith of Antarctic toothfish (Dissostichus mawsoni, TOA) across life stages by conventional measurement analysis, elliptical Fourier analysis and landmark method. The results showed that there were differences ontogenetically in otolith morphology. The shape of otolith changes from smooth and low complexity to intricate and high complexity, and the growth rate of otolith along the longitudinal axis is lower than that along the transverse axis. The characteristic parts, such as antirostrum, change significantly across life stages. Linear discriminant analysis showed the highest correct rate of classification is 85.417% from elliptical Fourier analysis, and followed by 79.167% from landmark method and 71.875% from geometric morphometrics, respectively.

In order to achieve the milestone “1.5 Update CASAL model” (SC-CAMLR-37 Report, Annex12), the CASAL models for Dissostichus eleginoides at Division 58.4.4b were revised.

We updated CASAL model with data up to 2019/20 fishing season. In this report, the base model (M1 model) is derived from the M4 model of previous report (SC-CAMLR-39/BG/51). We estimated the harvest rate (CAY and MAY) as defined in CASAL manual using each CASAL runs.

A single-sex age structured CASAL model using 5 cm bin for length distribution (M2 model) was built to assess the stock of constructed for D. eleginoides of the research block 1 of Division 58.4.4b. We updated data weighting values with latest data. Similar to the CASAL results reported previously (WG-FSA-2019/62, SC-CAMLR-39/BG/51), the MPD profile look good under both scenarios. It is noted that he MPD estimate values of B0 (M1: 870.54 tonnes, M2: 751.90 tonnes) are smaller than previously estimated in SC-CAMLR-39/BG/51 (ranging from 854 to 940 tonnes).

In both scenarios, estimated MCYs for D. eleginoides are higher than current catch limit 18 tonnes in block 1 at Division 58.4.4b. Harvest rates to achieve CCAMLR management target (50% B0), FCAY, were estimated to be close to 7%, which is higher than current precautionary harvest rate for explanatory fisheries where there is no estimate of B0.

This paper represents the final report of the multi-member longline survey on Patagonian toothfish (Dissostichus eleginoides) at Division 58.4.4b between 2016/17 and 2020/21 fishing seasons by Japan and France. The C2 and Observer data sets were provided by the CCAMLR Secretariat on July the 12th, 2021. In 2020/21 fishing season, both Japanese and French vessel could not conduct survey at Division 58.4.4b due to operational restrictions by COVID-19. This report mainly summarizes fishing activity and collected data. Although progress and achievements of each objective are reported, it is noted that there are ongoing studies that will be presented later in separate documents for future meetings.

This paper represents the final report of a multi-member longline survey on Antarctic toothfish (Dissostichus mawsoni) at Subarea 48.6 between 2018/19 and 2020/21 fishing seasons by Japan, Spain, and South Africa. This survey period is the third of three seasons research at the Subarea 48.6; 1^st: 2012/13-2014/15, 2^nd: 2015/16-2017/18, 3^rd: 2018/19-2020/21. The data set, C2 and Observer data, was provided by the CCAMLR Secretariat on the 14th July, 2020. This report summarizes fishing activity, collected data, and progress and achievements of each objective.

In this paper, the data set during current fishing season (2020/21) was used for reporting the quantity of data and samples collected. The research operations at 48.6 have not yet been completed in the 2020/21 fishing season.

A preliminary integrated stock assessment model was constructed for Dissostichus mawsoni at the Subarea 48.6, using the data collected from Research blocks 2 – 5. Our model showed some improvements, especially in the age/tagging related assumptions. On the other hands, we found some unexpected results on CPUE fits and MPD profiles, which should be carefully considered before we move on to the next step. Additional data or arrangement of parameters of CASAL model might help us to improve the model quality to conduct the future stock assessment of D. mawsoni in subarea 48.6.

We report the progress on the development of statistical modeling to estimate abundance trends of bycatch species (grenadiers) caught by longline fisheries in CCAMLR Subarea 48.6 using a spatial delta-GLMM implemented by the R package VAST. In response to the comments from WG-FSA-2020 e-group discussions, separate models were constructed for all research blocks within the subarea, and the residuals diagnostics were examined. Although we successfully estimated indices of abundance and the estimation was robust to the choice of covariates, further examinations and improvements are required, given the result of model diagnostics.

During three fishing seasons 2018/19, 2019/20 and 2020/21 Ukrainian vessel CALIPSO (shipowner FC NEPTUNO LLC, Ukraine) tried to perform the research survey in the statistical subarea 48.1 according to the research plans and annual management advices of the working groups FSA and Scientific Committee meetings. All three surveys were interrupted before the completion of research objectives. The first season of the research, the problem was concerned accessibility of fishing grounds due to sea-ice, the second and the third seasons of the research by-catch limit of Macrourus spp. was reached before the surveys were completed. Nevertheless, there were collected a large number of diverse scientific data on pelagic and benthic ecosystems, including high quality underwater footage, video monitoring of hauling lines and also photo and video fixation of tagged toothfish releasing.

Reducing fish and invertebrate by-catch in targeted fisheries is an element of a precautionary approach to the management of Antarctic living resources. At the same time establishing by-catch limits sometimes could block in fact the research activities in certain marine areas. It is  a reason to consider establishing by-catch limits for each separate research survey taking into account a research approach, abandoning the universal approach like reflected in the Conservation Measure 33-03.

The Scientific Committee considered the assessment of Dissostichus spp. in data-poor fisheries to be of a high priority (SC-CAMLR-XXIX, paragraphs 3.125 to 3.145). The use of different gear types for the implementation of a multi-Member research on Dissostichus spp. in East Antarctica (Divisions 58.4.1 and 58.4.2) in the seasons 2011/12 - 2017/18 is a critical factor for their   efficiency and reliability. In the context of the discussion of the Scientific Committee (SC-CAMLR-XXXVII p.3.338-3.144; SC-CAMLR-XXXVIII p. 318, 3.119; SC-CAMLR-XXXIX p.4.10) we propose the research program on Dissostichus spp by the  multi-vessels  in Divisions 58.4.1  for seasons 2021/22-2023/24 based on standardized   sampling longline gear  and survey stratified  design.